An inflator for an inflatable vehicle occupant protection device, such as an air bag, may comprise a pressure vessel containing inflation fluid under pressure. Such an inflator is disclosed in U.S. Pat. No. 5,348,344. In the inflator disclosed in the '344 patent, the inflation fluid is an ingredient in a mixture of gases. The mixture of gases further includes a fuel gas which, when ignited, heats the inflation fluid.
The inflator has an igniter containing a small charge of pyrotechnic material. When the air bag is to be inflated, the igniter is actuated electrically. The pyrotechnic material is then ignited and produces combustion products which, in turn, ignite the fuel gas in the pressure vessel.
The fluid pressure inside the pressure vessel is increased by the heat generated upon combustion of the fuel gas. When the increasing fluid pressure reaches a predetermined elevated level, the pressure vessel is opened. The inflation fluid then flows outward from the pressure vessel and into the air bag to inflate the air bag.